1. Field of the Invention
The present invention relates to a vibrating gyroscope, and particularly to a vibrating gyroscope for detecting a rotational angular velocity by utilizing a bending vibration of a vibrating body.
2. Description of the Prior Art
FIG. 5 is an illustrative view showing an example of a conventional vibrating gyroscope. A vibrating gyroscope 1 includes a vibrator 2. As shown in FIG. 6, the vibrator 2 includes a vibrating body 3 having, for example, a regular triangular prism shape. Piezoelectric elements 4a, 4b and 4c are formed respectively on three side faces of the vibrating body 3. The piezoelectric elements 4a and 4b are used for driving to generate a bending vibration to the vibrator 2, and for detecting to obtain a signal corresponding to a rotational angular velocity. The piezoelectric element 4c is used for feedback when the vibrator 2 is driven. Supporting members 5a and 5b are attached to a ridge line in the vicinity of nodal points of the vibrating body 3. The supporting members 5a and 5b are formed with metal lead and the like, and used for ground terminals.
Resistors 6a and 6b are connected respectively to the piezoelectric elements 4a and 4b. An oscillating circuit 7 and a phase correction circuit 8 are connected to the resistors 6a and 6b. The supporting members 5a and 5b used for ground terminals are connected to an intermediate point of source voltage. Output signals of the piezoelectric elements 4a and 4b are supplied to a differential circuit 9. In the vibrating gyroscope 1, a driving signal as shown in FIG. 7 is supplied to the piezoelectric elements 4a and 4b. The vibrating body 3 bends and vibrates in a direction perpendicular to the face of the piezoelectric element 4c by the driving signal. When the vibrating body 3 rotates on its axis, a vibrating direction of the vibrating body 3 changes by a Coriolis force. Thus, a difference is produced between output signals of the piezoelectric elements 4a and 4b. A signal corresponding to a rotational angular velocity can be obtained by measuring the difference between output signals of the piezoelectric elements 4a and 4b by the differential circuit 9. A rotational angular velocity supplied to the vibrator 2 can be detected by measuring the output signal of the differential circuit 9.
However, in the vibrating gyroscope, only half voltage A of maximum source voltage is supplied to the piezoelectric elements for driving as shown in FIG. 7, because the ground terminals are connected to the intermediate point of source voltage. In the case of using low voltage source such as dry cell, a vibration is not generated to the vibrating body satisfactorily. When a vibration is not generated to the vibrating body satisfactorily, a sensitivity of the vibrating gyroscope is deteriorated. A means for compensating the sensitivity is used by using an another circuits. However, when such means is used, S/N ratio is deteriorated.
Usually, the same driving signal is supplied to two piezoelectric elements for driving, and a driving signal component is not obtained from the differential circuit. However, when resonance characteristics of driving systems change due to a variation of circumferential temperature, there is a case that the driving signal component leaks from the differential circuit. In such case, a drift signal is obtained from the differential circuit in spite of supplying no rotational angular velocity, and resulting in error detecting of rotational angular velocity.